In the present program we plan to determine the structure and conformation by means of single crystal X-ray diffraction of the following types of molecules. We plan to study the structure and conformation and changes in conformation of a series of siderochromes and deferrisiderochromes in order to obtain a better understanding of the iron transport properties of these molecules through membranes in microbial organisms. Also the stereochemistry of the particular siderochromes will be determined. We plan to study non-planar peptide bonds, conformations, isomerism, cycloisomerism, cyclodiasteriomerism in groups of cyclic hexapeptides, lactams and ferrichromes and to apply those observations to antibiotics containing cyclic peptides and depsipeptides.